Worldwide consumption of dimethyl terephthalate (DMT) is projected to average to 3.97 million metric tons by 2012. DMT is an ester of terephthalic acid and methanol and is used in the production of polyesters, including polyethylene terephthalate and polytrimethylene terephthalate. DMT is also a primary ingredient used in the manufacture industrial plastics, automotive parts, films, fishing lines, and food packaging materials.
Traditionally, DMT production utilizes the esterification of terephthalic acid with methanol generated by catalytic homogeneous oxidation of paraxylene. For example, liquid paraxylene can be oxidized by air in the presence of a cobalt salt catalyst to form an oxidate containing p-toluic acid and monomethyl terephthalate, and esterification can be carried out in the presence of methanol to form DMT.
Trimellitic acid (TMA) is another commercially important product with applications as an intermediate in the chemical industry, including resins for powder coatings, inks, wire enamels, high performance plasticizers with low volatility, and engineering polymers for high temperature applications. TMA can also be dehydrated to produce trimellitic anhydride, which is another commercially important starting material for the production of polymers and chemical intermediates.
Traditionally, TMA is produced by oxidation of pseudocumene (1,2,4-trimethylbenzene). Terephthalic acid and isophthalic acid can be produced commercially by liquid phase oxidation of p-xylene or m-xylene in the presence of acetic acid as a solvent and of a catalytic system including cobalt, manganese and bromine.
These processes, like the processes for producing many other commercially important chemical precursors, intermediates, and products, can be undesirable due to a heavy reliance upon environmentally sensitive and non-renewable feedstocks (e.g., petroleum feedstocks), and their propensity to yield undesirable by-products (e.g., greenhouse gases, heavy metals, halogens, carcinogenic hydrocarbons). As such, a need exists for improved methods and systems that utilize renewable feedstocks to produce DMT, TMA, as well as other chemical products.
As described in U.S. Publication No. 2010/0314243 by Frost et al. and International Publication No. 2010/148049 by Frost et al., the disclosures of both of which applications are incorporated herein by reference in their entirety, DMT and TMA can be produced from muconic acid. In addition, muconic acid, also known as 2,4-hexadienedioic acid, due to its double bonds and diacid functionality, can undergo a wide variety of reactions. Many muconic acid derivatives are known, including lactones, sulfones, polyamides, polyesters, thioesters, addition polymers, and other compounds. Such compounds have a wide variety of uses, including use as surfactants, flame retardants, UV light stabilizers, thermoset plastics, thermoplastics and coatings. Thus, improved methods for biological production of muconic acid or muconate from renewable feedstock are highly desirable for producing DMT, TMA and other chemicals.